Control of wave length in wave guide and coaxial lines



June 9, 1953 N. col-IEN ET AL 2,641,702

CONTROL OF WAVE LENGTH' IN WAVE GUIDE AND COAXIAL LINES mea oct. 22.194s A T TOJPA/EY Patented June 9, 1953 vCONTROL OF WAVE LENGTH IN WAVEGUIDE AND COAXIAL LINES Nathaniel L. Cohen, Teaneck, Ladislas Goldstein,1

Weehawken, vand William Sichak, Lyndhurst; N. J., assignors, by mesneassignments, to International Standard Electric Corporation, New York,N. Y., a corporation of Delaware Application October 22, 1948, SerialNo. 55,862

. 1 f This invention relates to wave transmission systems and moreespecially to the art of controlling thewave length of propagated wavesin a' transmission medium.

In wide band transmission media such as coaxial transmission lines ordielectric Wave guides the wave length of electric energy is generallydetermined by the dimensions of the conductors and the insulating media.The speed of transmission is substantially constant so that at a Y givenfrequency the nodes and loops will be differently distributed along theline than at any other frequency. In many instances it is desired tohave the wave distribution constant along a line with changes infrequency of energy in the line. A particular example of such systems iswhen it is desired tofeed the antennas of an array, or' other loads,with a given phase relationship, regardless of wave length, overarelatively wide band. With the usual transmission system, an elaboratetuning means to vary the inductance or capacitance of the line isrequired to achieve this purpose.

It is an object of this invention to.- stabilize the Wave length ofWaves propagated along a wave transmission line even though thefrequency of the impressed wavesris varied.

Another object is to provide an arrangement for producing a stabilizeddirectional radiation pattern fro-m an antenna array fed from a Wavetransmission line, even though the frequency of the waves impressed onsaid line is varied.

Another object is to provide a method of controlling the Wave length ofwaves propagated along a transmission line of the coaxial or waveguidetype, by constituting a gaseous discharge plasma as part of the line,and controlling the 2 Claims. (CL. Z50-33.63)

electron density of the plasma to control thereby i the dielectricconstant of the said line.

A feature of the invention relates to a Wave transmission line havingincorporated therein a gaseous discharge of controllablecurrent densityY for stabilizing the wave length of variable frequency Waves impressedon said line.

Another feature relates toa Wave transmission line of the coaxial typeor Wave guide type, havl reference to. the following description of anembodiment of the invention taken in conjunction with the accompanyingdrawings, wherein:

Fig. l is awschematic representation of a typical radiation system towhich theA invention is applicable.

Fig. 2 is a longitudinal central cross-section of a coaxial transmissionline embodying the invention.

Fig. 3 is a sectional view of Fig. 2, taken along the line 3-3 thereof.l

Fig. 4 is a longitudinal central cross-section of a Wave guide embodyingthe invention.

In certain kinds of Wave transmission systems such, for example, asradiating antenna systems and the like, it is highly desirable toproduce a field or radiation pattern which has substantially constantdirectional properties, even though the impressed Waves are varied infrequency. Thus,

there is sho-Wn in Fig. 1, a typical antenna array comprising a coaxialfeed line With its central conductor l and its outer concentricconductor or pipe 2. Connected at suitable spaced points along thelength of conductor I, are the several radiator elements 3. Likewise,connected to the conductor 2 at the samespaced intervals are thecomplementary radiator elements 4. vThe showing of Fig. 1 is intended tobe generically schematic, in that the radiator elements are arranged toextract wave energy from the coaxial transmission line at appropriatenumerous points along its length. It will be understood, of course, thatthe radiator elements may be coupled to a Wave guide instead of acoaxial line, for the same purpose. The theory of such an arrangement isthat each set of radiator elements extracts small packets of energycontent from definitely phased points along' the line. Thus, for

example, the spacing interval between the sucing of the several radiatorelements, or of the frequency of the source 5 from Which the Wavesobjects of this invention and the manner of attaining themv Will becomemore apparentand the invention itself Will .be best understood,v by

are impressed on the line, will result in a shift in the direction ofradiation.

In certain cases, it is desirable to be able to operate such a systemover a wide range of impressed frequencies, for example from 1,0'00megacycles to 2,000 megacycles. Therefore, in

order to avoid any substantial shift in the radiation direction for thedifferent impressed frequencies, it is necessary to maintain the wavelength of the waves propagated along the line at l a stabilized selectedValue. The present invention provides a method and arrangement ofapparatus for securing this desirable objective.

It has been determined hereto-fore, that at high frequencies, thedielectric constant of a conductive gaseous discharge plasma depends onthe electronic charge density contained in the plasma, the plasma as iswell-known, constituting the largest portion of the discharge column. Y

between the anode and cathode of agaseous con-` duction tube. Therelation between thisY dielec-4 tric constant and the electronic chargedensity is given bythe following formula.;A Y

where Y eg is the effective dielectricv constant at frequency w/Z1r;

E is the dielectric'constantof free space;

Ne is the electronic charge densi-ty; and

is the ratio of charge to mass of the electron. In the case where theelectronic collisional frequency v in the discharge plasma is of theorder of or larger than the signal frequency w/21r, this expressionbecomes:

41|-Ne2 Elf- 1 However, for purposes of this discussion, we will omitthis case.

It is` also known that the wave length of a wave in dielectric medium isrelated to its free space wave length by: Y

where he, is the free space wave length;

M isjthewave length in the dielectric medium;

EdY is the relative dielectric constant of the medium.

In accordance with the present invention, the transmission feed lineYhas incorporated in the wave propagating spaced thereof a gaseousdischarge plasma of controllable electronic charge density. For example,in the case of a coaxial If we set M as a constant and with eo=l, Wehave Near-(til o That is, N, the electrondensity, is azfunction offrequency for a constant wave length )\=?\d. Now, it is known that N isa function of the current density, and hence the current in thedischarge, for a given set of conditi-ons of gas pressure, nature of thegas and gas purity and geometry. y

Referring to Figs. 2 and 3, there is shown a suitable .arrangementwhereby the wavelength of a signalin a coaxial line can be held constantover a wide range of transmitted frequencies. The line comprises theusual central conductor `6 and its coaxial guide or pipe conductor 1,a1'- ranged to be connected to a suitable high frequency source 8.Surrounding the conductor 6 and located within the wave propagationalspace ofthe coaxial line, is an elongated tubularglass container 9,having side seals I0 and II. Suitably mounted in the side seals I0 and II, are respective electrodes I2, I3, which are connected Y sure of a fewmillimeter of mercury. When theV electrodes I2' and I3 are thusenergized, there is set up a gaseous conduction column extendingthroughout the length of the tube 9, the greater part of this columnbeing constituted of ther plasma. By means of the source I4 and theadjustable resistor I5,v the current density inV the plasma can beadjusted to-flt the requirements of the above-noted formula #6. As atypical. example, if the impressed frequencies from source 8 arevariable between 1,000 mega-cycles and 2,000 megacycles, and it isdesired maintain the wave length in the line at 30 centimeters, which isa free space wave length of 1,000- megacycle signals, then from Formula#6 it can be seen that for f=1,000 meg acycles,'N=0- For a frequency of2,000 megacycles, N`=3.68 1010 electrons per cubiccentimeter within theplasma. Then for different frequencies between 1,000 megacycles and2,000v megacycles, the relation of the impressed frequency andlstabilized wave. length and the number of electrons per cubic centimeterin the plasma is given in thev follow--V ing table:

f M Y electrons/cc.

Cms. Cms.

Thus, it will be seen that by adjusting the current density in theplasma, the wave length can be stabilized at any particular value inaccordance with Formula #6.

In the event that the stabilization,l is to be ef-l fected.rautomatically, a sample of the energy propagated through the line can beapplied` to anyV well-known frequency discriminator I6 whose output cancontrol a variable resistor tube I'I connected acrossresistor I5'. VBythis arrange--A menttherefcre, the propagated Wave length in;

the coaxial line will be automaticallystabilized at the predeterminedvalue.

It will be clear that the invention is not limited to a transmissionliney of the coaxial type. Thus, there is shown in Fig. 4 a transmissionline of the Wave guide type wherein the Wave guide I9 has on theinterior thereof an elongated gaseous conduction tube i9 which may besimilar to tube 9 of Fig. 2. Here again, the current density in theplasma within the tube I9 can be adjusted by potential source 20 andvariable resistor 2i in accordance with the above-noted Formula #6 tostabilize the Wave length of the propagated Waves Within the Wave guide.It will also be understood that the transmission line with which thecontrolled plasma cooperates may be of any other Well-known type. v

While We have described abo-ve the principles of our invention inconnection with specific apparatus, it is to-y be clearly understoodthat this description is made only by Way of example and not as alimitation to' the scope of our invention.

What is claimed is:

1. A high frequency Wave transmission line, comprising a hollow memberdening a wavepropagating vline upon which high frequency Waves areimpressed, an enclosed gas-tight device extending along a predeterminedlength of the interior of said member, said device containing a fillingof an ionizable gaseous medium, electrodes at opposite ends of saiddevice, means to adjust the potential between said electrodes to controlthe density through said medium to stabilize the physicalwave length ofthe Waves propagated along said linev Within said medium, and aplurality of radiator elements'coupled to said Wave propagatinglinethrough the ionizing device at spaced points along said device, saidmeans to adjust being controlled to present the high frequency energy atthe same'relativephase to said radiators over av range of frequency of`said high frequency source.

2. Apparatus according to cla-im 1, in which said line is of the coaxialtype. NATHANIEL L. COI-IEN. LADISLAS GOLDSTEIN.

WILLIAM SICHAK.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,064,582 Wolff Dec. 15, 1936 2,106,770 Southworth Feb. 1,1938 2,142,648 Linden Jan. 3, 1939 2,159,937 Zworykin May 23, 19392,203,807 Wo-ln June 11, 1940 2,210,666 Herzog Aug. 6, 1940 2,407,250Busignies Sept. 10, 1946 2,408,425 Jenks et al. Oct. 1, 1946 2,408,435Mason Oct. 1, 1946 2,477,510 Chu July 26, 1949 2,480,208 Alvarez Aug.30, 1949 2,557,961' Goldstein et al. June 26, 1951 2,577,118V Fiske Dec..4, 1951

